RadDataForm Custom Editors

If you followed the getting started section, you now know how to edit an object's properties with RadDataForm for NativeScript. The editors list article demonstrated the available editors. This article will show you what to do if the editor you would like to use is not on the list with available editors. For example, if we wanted to have a Button to change the value of the property age in this example, we could use android.widget.Button in Android and UIButton in iOS.

Figure 1: RadDataForm with custom editor

NativeScriptUI-DataForm-Custom-Editors-Android

Create a custom property editor

In this article you will learn how to create a custom editor that uses native Button controls to change its value as in the screenshot above. First, you will need to set an instance of CustomPropertyEditor as the editor of the EntityProperty associated with the property of the source object that we want to edit with a custom editor (in our example this is the age property):

Example 1: RadDataForm with custom editor

<df:EntityProperty name="age" index="1">
    <df:EntityProperty.editor>
        <df:CustomPropertyEditor 
            editorNeedsView="editorNeedsView" 
            editorHasToApplyValue="editorHasToApplyValue" 
            editorNeedsValue="editorNeedsValue"/>
    </df:EntityProperty.editor>
</df:EntityProperty>

Here's the flow for the usage of the custom editor step-by-step:

RadDataForm loads and it needs a view that will be used for the custom editor - the editorNeedsView event occurs.
The original value of the property in our source object has to be loaded in the custom editor - the editorHasToApplyValue event occurs.
The user interacts with the provided editor view which changes the value of the editor - you have to call the editor's notifyValueChanged method.
RadDataForm needs the current value of the editor - the editorNeedsValue event occurs and we have to update the value of the property depending on the current value of the custom editor.

All aforementioned events are fired with arguments of DataFormCustomPropertyEditorEventData type.

Here's what we are expected to do in the handlers of each of the mentioned events:

The editorNeedsView event occurs when a view has to be placed inside our custom editor, so in our event handler we will create a native view depending on the current platform and set the result as value of the view property of the event data (On Android the event data will contain a context property with Context that we can use to create our View).
The editorHasToApplyValue event occurs when the value of the property has to be used as initial value of our editor. Here, we will just take the value of the value property and apply it as formatted text for the view provided with the view property.
The editorNeedsValue event occurs when we have to update the property value. This means that we will use again the view and value properties of the passed event data, but this time we will set the value depending on the value of our editor.

This is the Android implementation of the mentioned event handlers:

Example 2: Custom editor implementation for Android

let buttonValue;
export function editorNeedsView(args) {
    const editorView: android.widget.Button = new android.widget.Button(args.context);
    editorView.setOnClickListener(new android.view.View.OnClickListener({
        onClick(view: android.view.View) {
            handleTap(view, args.object);
        }
    }));
    args.view = editorView;
}

export function editorHasToApplyValue(args) {
    updateEditorValue(args.view, args.value);
}

export function editorNeedsValue(args) {
    args.value = buttonValue;
}

export function updateEditorValue(editorView, value) {
    buttonValue = value;
    editorView.setText(buttonValue + " (tap to increase)");
}

export function handleTap(editorView, editor) {
    const newValue = buttonValue + 1;
    updateEditorValue(editorView, newValue);
    editor.notifyValueChanged();
}

Notice that we called the notifyValueChanged method of the CustomPropertyEditor. This is necessary since the value change depends on the custom editor that we provide and thus it is our responsibility to notify RadDataForm for the update in the editor's value and in this example, the value change happens when the button is pressed.

Here's the iOS implementation of the same event handlers:

Example 3: Custom editor implementation for iOS

let buttonEditorHelper;
export function editorNeedsView(args) {
    buttonEditorHelper = new ButtonEditorHelper();
    buttonEditorHelper.editor = args.object;
    const editorView = UIButton.buttonWithType(UIButtonType.System);
    editorView.contentHorizontalAlignment = UIControlContentHorizontalAlignment.Left;
    editorView.addTargetActionForControlEvents(buttonEditorHelper, "handleTap:", UIControlEvents.TouchUpInside);
    args.view = editorView;
}

export function editorHasToApplyValue(args) {
    buttonEditorHelper.updateEditorValue(args.view, args.value);
}

export function editorNeedsValue(args) {
    args.value = buttonEditorHelper.buttonValue;
}

export class ButtonEditorHelper extends NSObject {
    public buttonValue: number;
    public editor: CustomPropertyEditor;

    public updateEditorValue(editorView, newValue) {
        this.buttonValue = newValue;
        editorView.setTitleForState(this.buttonValue + " (tap to increase)", UIControlState.Normal);
    }

    public "handleTap:"(sender) {
        const newValue = this.buttonValue + 1;
        this.updateEditorValue(sender, newValue);
        this.editor.notifyValueChanged();
    }

    public static ObjCExposedMethods = {
        "handleTap:": { returns: interop.types.void, params: [UIView.class()] }
    };
}

We have created a helper class which exposes a handleTap method that will be executed when the native button is tapped. This is explained in more details here. The rest is quite similar to the code we have in the Android implementation - editorNeedsView to create the native view; editorHasToApplyValue - to update the editor with the provided value and editorNeedsValue - to provide the value that the editor currently holds.

References

Want to see this scenario in action? Check our SDK examples repo on GitHub. You will find this and many other practical examples with NativeScript UI.

Custom Editors Example

NativeScript Core